The Islamic State (IS) extremist group has claimed responsibility for an attack on a police academy in southwestern Pakistan that left at least 61 people dead.

The group's Arabic-language Aamaq news agency said on October 25 that "Islamic State fighters" carried out the overnight attack in Quetta, the provincial capital of restive Balochistan Province, in which more than 100 people were also wounded.

Pakistani authorities blamed another militant group, Lashkar-e Jhangvi (LeJ), for the attack, though the IS claim included photographs of three alleged attackers.

The four-hour siege, which started late on October 24, was one of the deadliest attacks on Pakistan's security forces in recent years.

Officials said that five or six armed men had attacked the dormitory of the Balochistan Police College on the outskirts of Quetta where cadets were resting and sleeping, provoking a counterterrorism response from the army and Frontier Corps.

"Two attackers blew themselves up, while a third one was shot in the head by security men," said Sarfaraz Bugti, home minister of Balochistan. Bugti added that more than 200 of the 700 cadets at the academy were quickly rescued.

Prime Minister Nawaz Sharif and army chief General Raheel Sharif both traveled to Quetta on October 25 for an emergency security meeting.

Major General Sher Afgan, chief of the paramilitary Frontier Corps in Balochistan, which led the counterterrorism operation, blamed the attack on the Al-Alimi faction of the LeJ, which is affiliated with the Pakistani Taliban.

The LeJ, whose roots are in the heartland Punjab Province, has a history of carrying out sectarian attacks in Balochistan, particularly against members of the Shi'ite Hazara minority.

Pakistan has previously accused LeJ of colluding with Al-Qaeda, the IS group's rival. Balochistan is the scene of a low-level insurgency by Baluch separatists. Militant groups like the Afghan Taliban are also active in the province that borders Afghanistan.